Sophisticated, microprocessor based control systems for video cameras, still cameras and cine cameras have been developed together with advances in synchronized direct and indirect scene illumination systems for providing automatic exposure, automatic focus and, in the case of still cameras, automatic strobe flash illumination, mounted on or associated with the camera. The microprocessor based control systems for such cameras store operating algorithms for processing user interface and sensor developed signals and for developing imaging lens focus, image exposure, media (film or videotape) advance and illumination control signals as well as providing data and signals to the user. Such a highly developed automatic camera control system is disclosed in commonly assigned U.S. Pat. No. 5,049,916 to O'Such et al, incorporated herein by reference in its entirety.
The illumination of objects in a scene that is insufficiently lighted by natural or artificial indoor lighted is typically effected by a camera mounted or associated flood lamp, in the case of video or cine cameras, and the electronic strobe flash systems, in the case of still cameras. Electronic strobe flash systems mounted on or in a camera and involving the rapid discharge of a high voltage through a flash lamp synchronized with the exposure of an image frame are well-known in the photographic art. For indoor illumination of a scene, it is desirable to provide indirect lighting so that it appears to be illuminated from above in a way characteristic of natural lighting and to illuminate the scene directly to soften dark shadows caused by downwardly directed light.
In strobe flash illumination for still cameras, the indirect illumination is commonly known as "bounce" flash, since the light is typically directed upward and bounced off a reflective ceiling and onto the scene, although it is also known to bounce the flash light off a vertical wall or panel to provide side illumination. Flash light aimed directly at the scene is referred to as direct illumination or "fill-in" flash. Where natural illumination from above is available, such as in daylight outdoor scenes, direct or fill-in flash may be employed to soften shadows falling on the subject to be photographed. Conversely, in indoor scenes, where illumination from above is not available or does not possess natural light spectral characteristics, it is desirable to provide indirect illumination by bouncing flash light off a ceiling and onto the scene or subject to be photographed. In such situations, it is also desirable to provide direct illumination so as to again fill in shadows created by the downwardly directed bounce flash illumination. The combination of bounce and fill-in flash illumination minimizes the undesirable effects of direct illumination alone, including harsh shadows, red eye, specular reflections, and high contrast or loss of tonal detail depending on the distance of subjects in the image. Unfortunately, indirect flash illumination requires much more energy than direct illumination due to light intensity loss by absorption and scattering by the ceiling or wall surface.
U.S. Pat. No. 4,242,616 describes a photographic flash apparatus for providing both fill-in and bounce flash illumination provided by a direct illumination flash bulb 17 and an indirect illumination flash bulb 19, which are simultaneously charged from a single battery 20 and a discharge capacitor 23. The high voltage capacitor 23 is discharged simultaneously through the flash tubes 17 and 19 synchronously with the operation of the camera shutter. By configuring the direct and indirect flash tubes differently and choosing appropriate circuit components, bounce flash illumination provided by the indirect flash tube 19 exceeds the fill-in illumination provided by the direct flash bulb 17. The amount of illumination provided is measured by a photo detector aimed at the scene, and both fill-in and bounce flash light is terminated simultaneously when a desired total reflection of light from the scene is achieved. A ratio of indirect to direct illumination of about 75:25 is sought in the operating example of the circuit described in the '616 patent.
U.S. Pat. No. 4,384,238 discloses an electronic strobe flash apparatus for bounce and fill in flash illumination of a scene also having direct and indirect flash tubes coupled in parallel to a charging capacitor, battery, DC/DC converter, and control circuit and to separate quenching circuits for separately halting discharge through each of the flash tubes. In the flash apparatus of the '238 patent, the control circuit is switched into operation synchronously with the camera shutter release and first causes the indirect flash lamp to discharge and emit bounce flash illumination on the scene. During a 40 microsecond period, a photo detector circuit measures the light reflected from the scene and, if the reflected light falls below a certain threshold indicating the absence of a suitable reflective ceiling surface, the bounce flash illumination is quenched and fill-in flash illumination is simultaneously commenced. If, however, the bounce flash illumination reflected from the scene is sufficiently high, then bounce flash illumination continues until the reflected light reaches a second threshold, whereupon bounce flash illumination is quenched and fill-in illumination is commenced. The photo detector and control circuit continues to monitor the accumulated reflected fight and quenches fill-in illumination when the total measured illumination reaches a further threshold related to the film %W and shutter speed. The user may override the control circuit by disabling bounce flash illumination when there is sufficient overhead illumination or when no ceiling is present.
A further U.S. Pat. No. 5,136,312 to Weaver et al, assigned to the assignee of the present invention, describes a direct and indirect flash illumination system wherein the presence of a suitable reflective ceiling surface is detected by light reflected therefrom is employed to control the ratio of indirect and direct illumination and, in conjunction with light reflected from the scene, total illumination. In one embodiment, an active radiation emitter transmits IR radiation upward in a manner such that a portion of the radiation is reflected back to a photo detector which provides a first signal containing information relating to the distance between the surface and the flash system as well as the quality of the reflective surface. A control system responsive to the signal causes both bounce and fill-in flash illumination when the indirect reflecting surface is within a predetermined distance and causes operation of only fill-in or direct flash illumination when the indirect reflecting surface is not within the predetermined distance. The first signal and a further signal developed by a photodetector aimed at the scene are employed in controlling total illumination by separately quenching the direct and indirect illumination.
In an alternative embodiment, a photodetector aimed upward is employed in a passive mode to detect bounce flash illumination reflected back from the ceiling, if present, in order to provide the first signal under the circumstances previously described. Thus, the '312 patent discloses a system which determines the presence or absence of a suitable reflective ceiling by measuring light reflected therefrom and controls bounce flash illumination in dependence thereon. Variable flash output and aperture selection can be combined in a single system to match the optical depth of field with the depth of illumination provided by the bounce and/or fill-in flash illumination. A quick recycle mode is also disclosed wherein bounce flash illumination is suppressed. In the various disclosed embodiments, when bounce flash illumination is allowed, it commences simultaneously with fill-in flash illumination, and the illumination from both the direct flash tubes is quenched either simultaneously or in an order dependent on the detected light returning from the scene in accordance with known exposure control algorithms.
In a further U.S. Pat. No. 5,055,865 to Fujino et al, a pair of separately controlled direct and indirect flash apparatus are disclosed which may or may not be incorporated into the camera body wherein bounce and fill-in illumination are provided of a scene under a number of operating algorithms. Preferably, the fill-in illumination is provided by a direct flash lamp, battery, charging circuit and control circuit, all incorporated in the camera body, and bounce illumination is provided by an indirect flash apparatus having a self-contained battery, charging capacitor and micro-computer based control system which may be mounted to hot-shoe of the camera body as if the camera had no internal flash apparatus. The various modes of operation include a charging subroutine illustrated in FIG. 7 where it appears that charging of the external and internal flash apparatus high voltage capacitors is triggered simultaneously and the priority of direct and indirect flash illumination may depend on which capacitor charges up first. The speed of charging the high voltage capacitor of the internal flash apparatus may be affected by prioritized allocation of current drawn from the battery for powering other camera functions, such as automatic focus and motorized film advance as shown in FIG. 17.
In conjunction with direct and indirect illumination systems as described above, sophisticated cameras are also provided with various range finding systems for automatic focus (AF) adjustment of the camera imaging lens. As is well known in the art, the range finders employed in video and still cameras may be characterized as either active or passive. The active AF systems project infrared light or sound electromagnetic radiation from a position on the camera onto an object in the scene to be photographed and detects the reflected portion of the projected electromagnetic radiation. Passive range finders typically rely on ambient scene illumination, although it is known to provide a light emitting diode directed typically toward the center of the scene to augment the available scene illumination.
In AF control systems, the active and/or passive range finders provide signals from which the distance between the camera body and, typically, the subject or structure in the scene that the user has centered the imaging lens on may be determined and employed with a motorized servo-system to adjust the focal length of the imaging lens. Passive range finders employ one or more pairs of linear photo-diode arrays that are positioned end-to-end with respect to one another and a fixed distance apart which forms the baseline of the autoranging triangulation system. In triangulation AF systems, the baseline is a necessary dimension which allows for the formation of similar triangles used to calculate subject distance. Generally, as the baseline dimension and focal length increases and the linear sensor array width (pitch) decreases, the maximum sensing distance increases.
Typically, a pair of focusing lenses are positioned with respect to each pair of spaced apart linear photosensitive arrays to focus the image the camera is pointed at onto the linear arrays. In SLR camera systems, the focusing lenses are arranged symmetrically with respect to the optical axis of the camera's imaging lens and light passing through the lens (Tm) is diverted by half silvered mirrors through the pair of focusing lenses and onto the linear arrays. In range finder cameras, the pair of focusing lenses and the associated linear arrays of photosensitive elements are mounted end-to-end on the camera a distance away from the imaging lens.
The photo-electrically converted signals from the photosensitive elements of the linear arrays of a passive range finder are processed by the microprocessor based AF control algorithm to detect a displacement of the two images focused thereon and to provide an AF control signal to a motor which drives a gear mechanism to adjust the imaging lens focus. The -operation of a typical AF system is described in U.S. Pat. No. 4,643,557 to Ishizald et al (incorporated by reference herein in its entirety) and is referred to in the above incorporated '259 patent.
Active range finders typically include a radiation light beam source for emitting a beam of, for example, infrared radiation through a focusing lens in a direction aligned with the axis of the camera imaging lens and a two-area radiation sensitive element spaced a fixed distance away from the radiation emitting element and also having a focusing lens for focusing the infrared radiation reflected by an object in the scene onto the radiation sensitive element as shown, for example, in U.S. Pat. No. 4,518,242, to Toyama, incorporated herein by reference in its entirety. The focal point of the radiation emitting and detecting lenses are correlated to the focal point of the imaging lens, and, if the imaging lens is not in focus on the object from which the radiation is reflected, the reflected radiation is focused more favorably on one or the other of the two areas of the radiation sensitive element. The imaging lens is driven by a servo motor to change its focus as a function of the positive or negative out of focus deviation detected by the active auto range finding integrated circuit until the reflected radiation is imaged in a null zone between the two active areas of the two-part radiation sensor or is equally focused, in intensity, on both areas. Other tis of active range finders are known particularly for use with multiple lens camera systems, but all share the common components of an electromagnetic radiation emitter and detector and signal processing circuits for providing the servo control signal to drive the lens focal length adjustment motor and may be referred to as "single-spot" active range finders, since the emitted light beam is directed onto and reflected from a spot on the scene, typically the central portion thereof.
The active range finder is able to respond to objects of low brightness or low contrast (such as a blank wall). Additionally, because the signal to noise ratio of its signal becomes higher at shorter object distances, where the depth of field is shallow, the active type range finder generally has a high degree of accuracy. There are very few objects whose distances are impossible to measure with an active-type range finder. However, there are limitations in the ability of active range finders to measure objects of low reflectivity at far away distances because the projected energy of an active range finder radiation source cannot be increased as much as desired. Furthermore, if the active range finder radiation beam falls on a target that absorbs its energy (like the black stripe in a shirt), it may fail to detect the object. Additionally, the amount of electrical energy drawn by the active range finder radiation emitter presents a considerable load on the camera battery powering other camera systems.
Conversely, the passive-type range finder is not limited by object distance or object reflectivity contrast and consumes only a small amount of electrical power. However, it is almost impossible for the passive range finder to measure the distance to dim objects. Even where possible, the measurement may take a long time, e.g., half a second. Accordingly, there is a response gap in measuring distance, especially for moving objects. Moreover, the system algorithms become delayed due to the time necessary to carry out the integration of the measured signal. And, as stated above, passive range finders win fail to detect a low contrast target. As also stated above, it is known to extend the useable light level range of passive range finders by providing an infrared light emitting diode which may be energized at low light levels to illuminate the scene and speed operation of the passive range finder. Such illumination is directed at the center of the scene to illuminate the presumed subject of greatest interest. A passive range finder of the type described with available augmenting illumination is described in U.S. Pat. No. 4,992,817, incorporated herein by reference.
In view of these known complimentary strengths and weaknesses of active and passive range finder systems, cameras have been provided with both active and passive range finder systems used selectively or in combination to provide AE in both video and still cameras. See, for example, the following U.S. patents:
______________________________________ 4,518,242 Toyama 4,592,638 Kaneda, et al. 4,693,582 Kawamura, et al. 4,818,865 Matsui, et al. 4,835,561 Matsui 4,843,227 Matsui, et al. 4,992,817 Aoyama, et al. ______________________________________
The above listed patents disclose a variety of systems and algorithms for selecting and employing the active and passive range finders under a variety of conditions to take advantages of each range finder.
Referring again to the above-incorporated '916 patent, it sets forth the difficulties inherent in the selection and control of various combinations and alternative types of direct and indirect illumination and the selection of the appropriate lens aperture setting that provides sufficient depth-of-field to properly illuminate and expose the primary and background portions of the scene. In the '916 patent, a "multi-spot" passive range finder is focused on the renter, left and right portions of the scene to derive three sets of distance data from which the closest and most distant objects within the three portions of the scene may be employed to assess the "depth" of the scene. The scene depth data may be employed for both AE and AF control and taken into account in selecting the lens aperture setting when employing each type of illumination.
Multi-spot passive scene range finders are available in the form of multiple, e.g. 2 or 3, linear photosensitive element arrays arranged end-to-end to form a first array assembly which is associated with a first lens for focusing the left, central, and right portions of the scene on each respective array. An identical second array assembly and second lens, formed in the same fashion, is provided so that each respective array is positionally paired with its counterpart in the other array, and output signals Of each photosensitive element of each respective pair of arrays are processed as described above to provide two or three separate sets of AF control signals. As in the single array or "single spot" passive range finders described above, augmenting illumination may be provided, but doing so adds even further complexity since two or three separate light emitters and light directing lens elements may be necessary to illuminate each of the two or three portions of the lens. If a single light emitter is provided, it would be directed at the central portion of the scene so as to make the multi-spot array useable as at least a single spot array when such illumination is used.
The complexity, expense and current consumption of such highly automated cameras dictates the necessity of reducing the number of components and simplifying the operating algorithms wherever possible. The problem inherent in the incorporation of all of these automatic features into a single camera resides in the increased cost, complexity and current consumption.